FOSSIL REEFS AND TIME

Ariel A. RothGeoscience Research Institute

Origins 22(2):86-104 (1995).

WHAT THIS ARTICLE IS ABOUT

Ancient fossil reefs found within
Earth's sedimentary rocks are considered to be a challenge to the biblical concept of
creation. Their presence is regarded as favoring models which propose that life developed
gradually over many millions of years. The problem for the biblical model is that an
abundance of time is required to grow a reef and the hundreds of fossil reefs found would
require so much time to develop that they cannot be accommodated into the biblical time
framework of a recent creation a few thousand years ago.
Do these fossil reefs really negate the
biblical account of beginnings? There are alternative interpretations that do not require
long ages. For instance, these "reefs" may not be real reefs. There are serious
questions about the authenticity of many fossil reefs, because they differ significantly
from present reefs. Another possibility is that some fossil reefs could have been formed
between the time of creation and the flood described in the Bible, and were subsequently
buried by that world-wide catastrophe. Both alternatives seem plausible.

INTRODUCTION

Pilots of ships spend considerable time worrying about rocky
structures called reefs which lie at or just below the surface of the ocean. These reefs
are especially common in warm tropical seas, where coral, algae and associated organisms
slowly build these insidious structures which have caused many a ship to founder. Reefs,
sometimes called coral reefs, come in many sizes and shapes and represent some of our most
complex marine ecological systems.
Figure 1 illustrates a cross section of a typical reef. The reef core
is the most important part. It is a hardened structure, built up by living organisms, that
resists the pounding of the ocean's waves. On the ocean side of the reef core is the fore
reef, which consists of layers of sediment dipping towards the deeper ocean. These
sediments can: 1) originate from the reef core, 2) be produced by organisms living on the
fore reef, or 3) be brought in by ocean currents. On the back side of the reef, the reef
sediments underlie a shallow lagoon with calmer waters. The origin of the back reef
sediments is comparable to that of the fore reef. Sediment can also be washed in from a
land source or be precipitated by evaporation of the lagoonal sea water. Sometimes small
reefs called patch reefs will form as an accessory to a large reef complex (Fig. 1). Reefs
are built mostly of limestone (calcium carbonate).

FIGURE 1. Cross-section through a typical reef. The most significant part is the
reef core which is a hard wave-resistant structure built slowly by organisms. The core
supplies some sediments to both the fore reef and the back reef.

While the general picture given above leaves little question as to
what a modern reef is, the identification of a fossil reef is complicated by the fact that
there are similar structures which are formed in a different way. Especially noteworthy
are shallow-to-deep-water banks of sediment. These are formed mainly by the accumulation
of sediments transported by water currents. They are sometimes associated with organisms
such as eel grass that can facilitate the trapping and hardening of sediments. Such
structures can resemble a modern reef formed by the slow growth of living organisms.
Fossil reefs are the remains of ancient reefs. These are usually found
in the rocky sedimentary layers of Earth's crust. Occasionally, usually as a result of
erosion, fossil reefs are exposed at Earth's surface, where they are much easier to study.
The identification of fossil reefs is more difficult than that of present reefs. Problems
include: 1) the absence of the ocean, 2) the complex structures of reefs, 3) differences
in the reef-forming organisms compared to modern reefs, and 4) changes that take place
within the rocks over time. Because of economic reasons there has been considerable
interest in these fossil reefs. Many of them serve as good traps for oil; and the
scientific literature discussing them is voluminous. The general references by Braithwaite
(1973), Dunham (1970, 1972), Heckel (1974), James (1983), James and Macintyre (1985),
Rosen (1990), Scoffin (1987, p 77-88), Wilson (1975), and Wray (1971) are especially
pertinent to the broad questions being considered in this note.
There are problems with fossil reefs. They center on questions of
identification, structure, composition, and especially about how these ancient reefs were
formed. The terminology used to describe these is complicated by the fact that various
writers sometimes use the same terms in different ways. Some identification schemes are
based on structure and others on how the reefs are thought to have formed, or both. Heckel
(1974) notes that the terminology is particularly confusing "regarding terms that are
strongly genetic in meaning"; i.e., those terms that deal with the mode of origin.
For this and other reasons, a plethora of terms have been used to designate these ancient
reefs, including: ecologic reef, stratigraphic reef, bioherm, carbonate buildup,
allochthonous reef, autochthonous reef, true reef, reef mound, mud mound, bank, or knoll,
etc. The term "reef" itself has almost become too general a term for use in a
discussion of fossil reefs. It can specify any rock unit that seems to have been elevated
above its surroundings.

THE TIME QUESTION

Fossil reefs are of special interest when the question of origins is
being considered. The salient issue is the amount of time required to form these ancient
structures. If an abundance of time was required for these reefs to form, they are a
severe challenge to the biblical account of origins. The Bible describes the creation of
life by God during a six-day creation event which took place a few thousand years ago. The
Bible goes on to describe a world-wide flood which occurred well over a millennium later,
and lasted about one year. In the biblical context, this flood accounts for most of the
fossiliferous sedimentary layers of Earth's crust. If the sedimentary layers and their
varied fossils were laid down over millions of years, as is commonly interpreted, they
challenge both the creation and flood accounts given in the Bible. If fossil reefs found
in these layers formed at the slow rate at which we see present reefs forming (Roth 1979),
at least scores of thousands of years would be required to produce the superimposed fossil
reefs found in the fossil record. Is the biblical concept of a recent creation in error,
or is the geologic interpretation of fossil reefs in error? Both concepts cannot be
correct.
This discussion will focus on the rate of formation of these fossil
reefs. Specifically, did they form as a result of a slow biological process by
reef-producing organisms, as is noted for present living reefs, or do they represent rapid
accumulations of sediments transported and deposited by the waters of the Genesis flood?
In the context of this question it will be convenient for us to identify two main types of
reefs (James 1983). Allochthonous reefs designates reefs considered to have been
formed by the transport of sediment. Their formation can occur rapidly, but not
necessarily so. In contrast autochthonous reefs designate reefs that have formed
as a result of slow biological activity. These reefs can only form slowly. Allochthonous
reefs can be accommodated into the biblical model of a recent creation. Only under special
circumstances, which will be discussed later, can any autochthonous reefs be so
accommodated.

THE FOSSIL REEF RECORD

Hundreds of fossil reefs are reported throughout much of the
geologic column, starting from very low (Precambrian) sedimentary layers to the present
(Heckel 1974; James 1983, p 387-425; James and Macintyre 1985, p 37-47; Wilson 1975).
These reefs, with notable exceptions, tend to be different from present reefs (Ladd 1950;
Hodges 1987). They are often much smaller; some only in the meter range, and they are
usually produced by different kinds of organisms than those that build the present reefs.
The lowest (Precambrian) reefs in the geologic column are thought to be
produced by the mechanical trapping of sediments and the chemical action of various kinds
of microorganisms living on their surfaces. These structures represent a kind of laminated
deposit called stromatolite. Various forms and combinations of stromatolites are reported
as reefs.
Also located in the lower part of the geologic column (Cambrian) are
reefs that are produced by sponge-like organisms called archaeocyathids. They differ from
any presently known living organisms.
Higher up in the geologic column (Ordovician, Silurian, and Devonian),
are some larger more significant reef-like structures with reported ecological
developmental sequence and an organization into reef core and flank beds which dip away
from the core (see Devaney et al. 1986 for discussion). Some reef descriptions include
back reef lagoonal deposits. The most common organisms found in these reefs are sponges,
including peculiar laminated stromatoporoids. Coral organisms that are different from
modern corals are sometimes moderately abundant. Algae and bryozoa (moss animals) are less
important. Some of the organisms in the reef cores appear to be in position of growth
(e.g., Manten 1971, p 83, 435-438; Hodges and Roth 1986) while others do not (e.g., Heckel
1974, Wengard 1951). The orientation of the fossil in a reef is an important indicator of
whether the reef formed by allochthonous or by autochthonous means. A position of growth
suggests a slow autochthonous growth process, while unoriented fossils reflect an
allochthonous transport process. Unfortunately the identification of what is in growth
orientation has too often turned out to be quite subjective. Also, allochthonous blocks of
reef material can contain fossils in apparent growth position.
In this same part of the geologic column we also find many mounds of
fine lime (calcium carbonate) mud with few fossils (see Hodges 1987). Since coral reefs
are composed of lime, these mounds are of considerable interest. Mud mounds could
accumulate quite rapidly by an allochthonous transport of sediment.
A little higher up in the geologic column (Carboniferous) one also
finds a number of large sedimentary mounds composed of fine lime sediment sometimes with
crinoid fossil deposits flanking their steep sides. These enigmatic structures, which
range from many meters to kilometers in size, are called Waulsortian mounds  so
named after mounds located near the village of Waulsort in Belgium. Aggregations of such
mounds have been interpreted as a large barrier reef complex which would be expected to be
subjected to significant wave activity. But a question remains as to how much pounding by
waves these fine- sediment structures could withstand.
Higher in the geologic column (Permian through Jurassic) small to huge
structures interpreted as reefs have been described. The organisms that presumably formed
them are again different from those forming modern reefs. In addition to sponges, there
are relatively small amounts of algae, coral, bryozoa, and a problematic tube-like
organism called tubiphytes.
Some bizarre, but now extinct, bivalve molluscs called rudists form
reef-like structures near the upper part of the geologic column (Jurassic and Cretaceous).
Coral is occasionally found among the rudists (e.g., Scott et al. 1990). Rudists (Fig. 2)
are elongated, clam-like molluscs that have one shell somewhat similar in shape and size
to an ordinary clam shell, while the other can be very long, sometimes up to 1.5 meters in
length.

FIGURE 2. Rudist fossils from a rudist reef in central Texas. Note the coin for
scale. Many of the circular structures are cross sections of the elongated rudist mollusc
shells. The elongated fossils represent tangential or longitudinal sections.

In the upper part of the geologic column (Cenozoic), fossil reefs
are not very abundant. The associated organisms are mainly coral and algae, similar to
those forming modern living reefs.

CHANGING INTERPRETATIONS OF FOSSIL REEFS

Because fossil reefs and their past environment are difficult to
identify, and because they are so varied in composition and structure, it is not
surprising that interpretations of these challenging sedimentary structures are sometimes
revised. Four examples follow.

The Permian Reef Complex

The huge Permian
(Capitan) Reef is among the most, if not the most, studied fossil reefs. Located in the
southwestern United States, this ring-shaped reef has a diameter of around 200 kilometers,
and a length of over 700 kilometers. Most of the reef lies underground; however, about 40
kilometers of it are well exposed in the Guadelupe Mountains of Texas and New Mexico. The
upper portion of Figure 3 shows the lighter massive reef core. This core overlies the fore
reef beds that dip downward to the right. In this reef configuration the ocean is
considered to have been in the middle of the ring (right), while the back reef is around
the outside (left). The world-famous Carlsbad Caverns is dissolved right out of the reef
core of this reef.

FIGURE 3. View of part of the huge Permian (Capitan) Reef exposed in the Guadelupe
Mountains of Texas and New Mexico. The massive white cliff at the top of the picture is
interpreted as the reef core, while the bedded layers which dip to the right are
interpreted as the fore reef.

Interpretations of this structure have had a long and varied history
(Cys et al. 1977, Wood et al. 1994). In general, during the earlier part of this century
the Permian Reef was considered to be a true autochthonous wave resistant barrier type of
reef (e.g., Lloyd 1929, Hayes 1964, King 1948, Newell et al. 1953, and Newell 1955).
However, as early as 1937, Lang began to question the barrier reef concept. During the
past four decades a host of authors have questioned the traditional reef interpretation,
opting instead for some kind of deposit in deeper water (e.g., Achatier 1969; Cys et al.
1977; Dunham 1972; James and Macintyre 1985, p 40; Pray 1977; Babcock and Yurewicz 1989).
However, recently Kirkland-George (1992) and Kirkland-George and others (1993) have
revived the old barrier reef model on the basis of the location of some fossil algae that
are considered to require a lagoonal environment. In order to have a lagoon there must be
a barrier reef.
One of the main problems with the traditional reef interpretation of
the Capitan Reef complex is the lack of reef frame builders. The massive reef core
consists mainly of fine, calcium-carbonate mud (Fig. 4). The robust wave-resistant reef
frame builders of our present reefs are missing. There are some sponges but sponges are
not known to produce great reefs; and there is insufficient algae to bind the sediments. A
number of the sponges are bottom side up, interpreted as growing downward from the top
surface of cavities in the reef core (Wood et al. 1994). In order to have cavities, the
reef structure would have to be formed first. Because of the abundance of fine sediments,
many investigators have concluded that this is not a reef. It is considered to be an
underwater mud bank formed by the accumulation of fine sediments in deeper and quieter
waters. Some authors, such as Pray (1977) argue that the "reef" was always below
the surface of the ocean. The mud bank interpretation fits better with an allochthonous
interpretation than with an autochthonous one.

FIGURE 4. Photomicrograph of sediments from the reef core of the Permian (Capitan)
Reef. Note small circular and elongated fossil pieces. The photo is approximately 25 times
normal size.

A second major problem with the reef concept is that higher
sedimentary layers behind (back reef area) the reef core dip down towards the core and are
associated with the core in a way which indicates that the core must have been below the
surface of the ocean when it and the associated higher sedimentary layers were formed.
Accordingly, the reef core was not a wave-resistant structure. Several lines of evidence
indicate that this relationship is not merely due to tilting of sediments after deposition
(Hurley 1989, Yurewicz 1977, Babcock and Yurewicz 1989).

The Steinplatte Reef

In the High Calcareous
Alps of western Austria lies the famous Steinplatte Reef. This fossil (Triassic) reef
forms a dramatic barren limestone cap that stands above the wooded hillsides. When viewed
from the west (Fig. 5), the main cliff of exposed limestone represents the fore reef. The
reef core lies behind and on top of the cliff. The reef has been studied for over a
century. Fossils are abundant, but do not present a convincing picture of a defined reef
structure. There have been at least three major studies, each giving different locations
for the main parts of the reef (Piller 1981). More recently a geologist restudied the
Steinplatte Reef (Stanton 1988) and pointed out the lack of a biological skeletal
framework necessary to build a wave-resistant reef. He characterized the so-called
Steinplatte Reef as a "sandpile," and commented further that "The
Steinplatte is not an ecologic reef nor is it easily considered a reef by any other
definition." A sandpile could represent allochthonous deposition.

FIGURE 5. View from the west of the Steinplatte Reef in western Austria. What is
considered to be the fore reef is the whitish cliff above the wooded hillsides. It is
partially hidden by the clouds. The reef core lies behind the visible fore reef.

Nubrigyn Algal Reefs

The Nubrigyn
Formation is found in the lower part of the geologic column (Devonian) that is exposed in
eastern Australia. This formation has gained international prominence (Conaghan et al.
1976, Percival 1985) as a classic example of reefs formed by algae. Wolf (1965a,b,c,)
reports on several hundred algal reefs from this region. His interpretation has been
restudied (Conaghan et al. 1976, Mountjoy et al. 1972), and an entirely different
interpretation has been proposed. These algal reefs do not represent autochthonous
structures that grew where found. They represent part of a massive debris flow that
carried blocks as large as 1 km across. Evidence for an allochthonous origin includes a
variety of kinds and sizes of rocks mixed into a dark clay matrix, as would be expected
from a massive debris flow, and evidence for breaking of the rocks in transport, as seen
by their sharp edges (Fig. 6).

FIGURE 6. Debris flow of the Nubrigyn Formation of eastern Australia. Note the
variety of kinds of rocks floating in a dark clay matrix as expected for a debris flow.
Also note the broken edges on the whitish limestone block to the left indicating vigorous
transport. The coin to the left gives the scale.

Muleshoe Mound

The Muleshoe Mound
(Carboniferous) is illustrated in Figure 7. It is one of a number of similar structures
found in southern New Mexico (Laudon and Bowsher 1941). Muleshoe Mound is about 100 meters
thick. It represents one of the many Waulsortian mounds formed of fine lime mud mentioned
earlier. Various names such as bioherm, carbonate buildup, mound or reef (Heckel 1974)
have been applied to these enigmatic structures. Bolton et al. (1982) and Wilson (1975, p
148-168) review some of the scientific literature written about these. These mounds are
characterized by a core composed mainly (50-80%) of calcium carbonate mud. Some are
spectacularly conical with relatively steep sides. In some mounds, the mud core gives
evidence of bedded layers (Cotter 1965, Giles 1995) which can suggest transport of
sediments. Pray (1965) has described the intrusion of dikes into these mounds coming from
soft sediments below them. This indicates that the layers below were still soft when the
intrusion took place. (See Hornbacher 1984 and Roth 1992 for related information.)

FIGURE 7. Muleshoe Mound, a Waulsortian lime deposit from the Sacramento Mountains
in New Mexico.

Early interpretations of these puzzling structures suggested some
kind of autochthonous biological buildup, probably by crinoids, algae or bryozoa (Pray
1958; Wilson 1975, p 160-166), but the scarcity of such fossils is a problem. Some have
suggested inorganic cementation (Pray 1969). The most accepted model probably is that
these mounds were formed by the slow allochthonous accumulation of fine, water-transported
sediments. This accumulation is often postulated to have taken place in deep water below
the level of destructive waves. Location of the mound at the base of an underwater slope
which could serve as a source of sediment is also favored (Heckel 1974; Wilson 1975, p
165). Giles (1995), in studying Muleshoe Mound, has proposed formation by "massive
slope failure of rapidly accumulated sediments." Semi-coherent "glide
blocks" representing the core which had slid downslope were then flanked by debris
flows and turbidites. These flanking sedimentary layers could also be deposited rapidly.

EVALUATION OF FOSSIL REEFS

While most paleontologists accept the concept that fossil reefs are
true reefs, there is ample room for doubt. Rosen (1990) states that "Various fossil
structures have come to be called reefs simply because their features seem to
include framework or relief, in the absence of clear evidence to the contrary."
Lowenstam (1950, p 438) also expresses concern about lack of evidence when he states:
"we find in many reef studies that, once we are past the definition, the evidence is
too often so inadequate that the reader remains in doubt as to whether or not the author
was dealing with true reefs." Others "have expressed frustration at using modern
reefs to interpret their ancient counterparts" (Hubbard et al. 1990).
The identification of ancient stromatolites mentioned earlier has also
been controversial. The sedimentologist Ginsburg (1991) points out that "Almost
everything about stromatolites has been, and remains to varying degrees,
controversial." Stromatolite specialist Hoffman (1973) notes: "Something that
haunts geologists working on ancient stromatolites is the thought that they might not be
biogenic at all." If they are not biogenic, they would not necessarily be restricted
to a slow autochthonous biological process. Questions have also been raised about the
peculiar rudist reefs formed by the elongated molluscs referred to above. Gili et al.
(1995) "dispute [the] ... assertion ... that rudist formations commonly developed as
reefs." It is their opinion that "individual rudist congregations are
volumetrically limited, relative to sediment. They are often loosely constructed, and they
evidently showed little, if any, original relief" (see also Skelton et al. 1995). In
the rudist reefs of central Texas, the organisms in the reef core, which would be expected
in growth position are described in "random position"; while the organisms in
the flank beds, which are more subject to transport and which might be expected to be more
in random position, are reported in "growth position" (Robertson 1972). All of
these factors raise questions about the authenticity of autochthonous rudist reefs.
As noted above, reinterpretations of fossil reefs are not uncommon.
Some of the reinterpretations reflect the newer trend in geology towards catastrophic
interpretations that allow for rapid geologic changes. This is in contrast to the older
uniformitarian concept which emphasized slow gradual changes and probably favored an
autochthonous interpretation of many ancient reef-like structures. Mountjoy et al. (1972)
published information that reflects the trend towards catastrophism. They report on four
ancient reef-like structures (including the Nubrigyn reef) that have been reinterpreted as
debris flows. Debris flows form rapidly.
Probably the most important problem with fossil reefs is the usual
absence of organisms that would form a wave-resistant framework for the reef. Without this
framework, there is no guarantee that the reef took a long time to grow. The
sedimentologists Blatt, Middleton and Murray (1980, p 447) comment on the problem:

Closer inspection of many of these ancient carbonate 'reefs' reveals that
they are composed largely of carbonate mud with the larger skeletal particles 'floating'
within the mud matrix. Conclusive evidence for a rigid organic framework does not exist in
most of the ancient carbonate mounds. In this sense, they are remarkably different from
modern coral-algal reefs.

Skeletal particles floating in a mud matrix could result from relatively rapid
transport as in a debris flow.

FOSSIL REEF TRANSPORT

There is little question that there are major problems with the
identification of fossil reefs. However, can one be sure that there are no authentic
autochthonous reefs anywhere in the fossil record? One single fossil reef that would
normally have taken many years to grow could negate the biblical account of beginnings
with its requirement that most of the fossiliferous layers be deposited during the year of
the flood. To recheck all identified fossil reefs would not be an easy task, and would
require more than a lifetime. Earlier in this paper reference was made to reports of
fossil reefs with frame builders in apparent position of growth. These appear as true
autochthonous reefs. However, another alternative that would fit with the creation concept
is that some of these reefs grew that might have grown between the time of creation and
the flood. They could presently be in the position where they grew, or they may have been
massively transported during the upheaval of the flood.
Several investigators have referred to the transport of entire or major
parts of reefs (Cook et al. 1972; Heckel 1974; Hodges and Roth 1986; Newell et al. 1953,
Plates 14-2 and 15-1). The more recent interpretations of the Nubrigyn and Muleshoe fossil
"reefs" discussed above suggest massive transport. Polan (1982) found that
assumed autochthonous "bioherms" (reefs) in northern Canada were "blocks
derived during catastrophic events." The same kind of reinterpretation applies to
"patch reefs" of the Bone Spring Limestone in western Texas (Pray and Stehli
1963).
The new theory of plate tectonics with moving continents and changing
ocean floors has added further impetus to concepts of moving reefs. It is a relatively
minor event to move a reef compared to moving a continent. In some cases both can be
related. For instance, a number of fossil reefs have been described in the Austrian Alps.
The Steinplatte described above is one of these. Figure 8 shows another famous fossil reef
region of the Austrian Alps. It has long been suggested by geologists that these reefs and
their surrounding sedimentary layers came from an ancient Tethys Sea to the south, pushed
to the north as Africa moved towards Europe. How far these sediments and their reefs
traveled has been a matter of conjecture, but recent estimates (Tollmann 1987) suggest as
much as 1000 kilometers.

FIGURE 8. Looking south into the Dachstein Limestone above Lake Gosau in the
Austrian Alps. The vertical cliffs, to the right above the lake, are interpreted as a reef
complex. Some current interpretations suggest that this entire limestone formation has
been transported 1000 kilometers from the south.

Also to be considered within a creation context is the possibility
that some fossil reefs formed between creation and the flood have not moved with respect
to their immediate surroundings. They are presently located where they grew. An example
may be the extensive (Devonian) reef complex of the Canning basin in western Australia
(Playford 1980). This complex rests on basement (Precambrian) rocks. Should this complex
turn out to be a real autochthonous structure, it may represent a fossil reef that grew
during the many centuries before the Genesis flood, and it still rests on the basement
rocks where it grew.

CONCLUSIONS

It does not appear that fossil reefs present an undebatable time
problem for the biblical scenario of a recent creation. Their identification is often
questionable. Many fossil reefs are different from our present reefs, with 1) a different
configuration, 2) different kinds of organisms involved in their formation, and 3) a
notable absence of the rigid biological framework necessary for producing a real wave
resistant reef structure. These structures could be allochthonous, and as such do not
present the serious long-time challenge that slowly growing biological structures present.
They could have been formed by various kinds of sediment transport events during the year
of the Genesis flood. Some fossil reefs appear to be real autochthonous reefs, and may
represent reefs that grew between creation and the Genesis flood. Autochthonous reefs may
or may not have been moved during some of the catastrophic changes of that complex flood
event.

Hayes PT. 1964. Geology of the Guadalupe Mountains, New Mexico.
US Geological Survey Professional Paper 446.

Heckel PH. 1974. Carbonate buildups in the geologic record: a
review. In: Laporte LF, editor. Reefs in time and space: selected examples from the recent
and ancient. Society of Economic Paleontologists and Mineralogists Special Publication
18:90-154.

Hubbard DK, Miller Al, Scaturo D. 1990. Production and cycling
of calcium carbonate in a shelf-edge reef system (St. Croix, U.S. Virgin Islands):
applications to the nature of reef systems in the fossil record. Journal of Sedimentary
Petrology 60:335-360.

Pray LC. 1969. Micrite and carbonate cement: genetic factors in
Mississippian bioherms. Abstracts of papers to be presented at the North American
Paleontological Convention, September 5,6, & 7, 1969. Journal of Paleontology 43:895.